U.S. patent number 3,627,072 [Application Number 04/830,711] was granted by the patent office on 1971-12-14 for plural output path torque transmitting mechanism--hydraulic clutch for four wheel drive vehicles.
This patent grant is currently assigned to Borg-Warner Corporation. Invention is credited to Richard L. Smirl.
United States Patent |
3,627,072 |
Smirl |
December 14, 1971 |
PLURAL OUTPUT PATH TORQUE TRANSMITTING MECHANISM--HYDRAULIC CLUTCH
FOR FOUR WHEEL DRIVE VEHICLES
Abstract
A multiple output path drive system for a vehicle having plural
pairs of traction wheels including a torque transfer mechanism
adapted to receive an input torque which incorporates a
differential gear mechanism adapted to distribute the input torque
to a plurality of drive axles and a fluid pressure responsive
clutch between the differential gear mechanism and at least one
drive axle in fluid communication with a pressure source of an
automatic transmission, the clutch and fluid pressure source
adapted to urge the clutch into a fully engaged condition only when
the transmission is in a forward mode of operation.
Inventors: |
Smirl; Richard L. (La Grange
Park, IL) |
Assignee: |
Borg-Warner Corporation
(Chicago, IL)
|
Family
ID: |
25257538 |
Appl.
No.: |
04/830,711 |
Filed: |
June 5, 1969 |
Current U.S.
Class: |
180/249;
180/24.09; 475/86; 192/3.57; 475/225 |
Current CPC
Class: |
B60K
17/3462 (20130101) |
Current International
Class: |
B60K
17/346 (20060101); B60K 17/344 (20060101); B60k
017/34 () |
Field of
Search: |
;180/44,22K,24.09 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Levy; A. Harry
Claims
What is claimed is:
1. A multiple path drive system for a vehicle having at least two
pairs of traction wheels, a transmission conditionable for either
forward or reverse drive and a plurality of drive axle assemblies
including a plurality of torque transmitting members, each of said
members connected to an axle assembly; a torque transfer mechanism
comprising driven means for receiving an input torque from said
transmission, a differential gear mechanism connected to said
driven means including an input element driven by said driven means
and a pair of output elements driven by said input element, said
differential gear mechanism allowing relative rotation between said
input element and each of said output elements, clutch means
associated with at least one of said output elements, said clutch
means including a driving member connected to said one of said
output elements, a driven member connected to one of said torque
transmitting members, and a pressure applying means actuable to
urge said clutch means into an engaged condition; a source of fluid
pressure associated with said transmission; means for receiving
fluid pressure from said pressure source; valve means associated
with said transmission operative when said transmission is
conditioned for forward drive to direct fluid from said pressure
source to fluid pressure receiving means and means connected
between said fluid pressure receiving means and said pressure
applying means such that fluid pressure is communicated to said
pressure applying means to engage said clutch when said
transmission is conditioned for forward drive.
2. A multiple path drive system as in claim 1 including one-way
driving means disposed between any two elements of said
differential gear mechanism and adapted to allow relative overspeed
of one of said elements with respect to the other in a single
direction of rotation.
3. A multiple path drive system as in claim 1 including one-way
driving means disposed between said input element of said
differential gear mechanism and said output element associated with
said clutch means, said one-way driving means allowing relative
overspeed of said output element with respect to said input element
in a single direction of rotation.
4. A multiple path drive system as in claim 1 including a drive
chain connecting said driving member to one of said output
elements.
5. A multiple path drive system as in claim 1 in which said
differential gear mechanism includes a planetary gear set, said
input element comprising a planetary carrier driven by said driven
means, and a plurality of planet gears on said planet carrier, said
output elements comprising a ring gear and a sun gear meshing with
said planet gears and driven by said planet carrier and said planet
gears.
6. A multiple path drive system as in claim 1 in which said clutch
means includes at least one friction surface associated with said
driving member and at least one friction surface associated with
said driven member.
7. A multiple path drive system as in claim 1 in which said
transmission includes a hydraulic pump and a forward clutch wherein
said source of fluid pressure is said hydraulic pump and said fluid
pressure receiving means is said forward clutch.
8. A multiple path drive system for a vehicle operable in either
forward or reverse directions, said vehicle having at least two
pairs of traction wheels and an automatic transmission including a
source of hydraulic pressure, said transmission conditionable for
either forward or reverse drive, said multiple path drive system
including a plurality of drive axle assemblies; a plurality of
torque transmitting members, each of said members connected to an
axle assembly; a torque transfer mechanism comprising driven means
for receiving an input torque from said transmission, a
differential gear mechanism connected to said driven means
including an input element driven by said driven means; a first
output element driven by said input element and connected to one of
said torque transmitting members, a second output element driven by
said input element and connected to the other of said torque
transmitting members, said differential gear mechanism dividing
torque between said pairs of traction wheels in a ratio
relationship thereby allowing differentiation between said first
and second output elements, one-way driving means connected between
any two elements of said differential gear mechanism whereby when
one of said elements overspeeds the other element, said one-way
driving means locks said elements together for rotation permitting
no differentiation therebetween but when said other element
overspeeds said one element, a ratio relationship exists between
said output elements for any speed variations, a rotary drive
element connected to said second output element, a driven element
driven by said rotary drive element, a driving element connectable
to said one of said torque transmitting members, clutch means
associated with said driven element and said driving element;
means for receiving hydraulic pressure from said hydraulic pressure
source; valve means associated with said transmission operative
when said transmission is conditioned for forward drive to direct
hydraulic fluid from said pressure source to said pressure
receiving means and means connected between said pressure receiving
means and said clutch means such that hydraulic pressure is
communicated to said clutch means to urge said clutch means into a
fully engaged condition only when said transmission is conditioned
for forward drive.
9. A multiple path drive system as in claim 8 in which the one-way
driving means are disposed between said input element of said
differential gear mechanism and said output element associated with
said clutch means, said one-way driving means allowing relative
overspeed of said output element with respect to said input element
in a single direction of rotation.
10. A multiple path drive system as in claim 8 including a drive
chain connecting said driving member to one of said output
elements.
11. A multiple path drive system as in claim 8 in which said
differential gear mechanism includes a planetary gear set, said
input element comprising a planetary carrier driven by said driven
means and a plurality of planet gears on said planet carrier, said
output elements comprising a ring gear and a sun gear meshing with
said planet gears and driven by said planet carrier and said planet
gears.
12. A multiple path drive system as in claim 8 in which said clutch
means includes at least one friction surface associated with said
driving member and at least one friction surface associated with
said driven member.
13. A multiple path drive system as in claim 8 in which said
transmission includes a forward clutch wherein said fluid pressure
receiving means is said forward clutch.
14. A multiple path drive system as in claim 1 including first and
second fluid circuits connected between said valve means associated
with said transmission and said clutch applying means whereby said
valve means is operative to direct fluid pressure from said
pressure source to said first fluid circuit when said transmission
is conditioned for forward drive and to direct fluid pressure from
said pressure source to said second fluid circuit when said
transmission is conditioned for reverse drive.
15. A multiple path drive system as in claim 14 in which said
second fluid circuit includes second valve means adapted to
substantially decrease the pressure transmitted from said pressure
source to said clutch applying means.
Description
SUMMARY OF THE INVENTION
This invention relates to multiple path drive systems, for example,
a four wheel drive system, and more particularly, to a system
including a torque transfer mechanism adapted to receive an input
torque from a prime mover and to transmit torque to a plurality of
drive axles. The torque transfer mechanism includes a differential
mechanism having a pair of output shafts each of which is adapted
to be connected to a drive axle.
It is well recognized in the art that the tractive efforts of a
vehicle are substantially improved if driving torque is applied to
more than one drive axle. This concept underlies the employment of
known four wheel drive systems in military vehicles or trucks
intended for operation over unimproved terrain. However, certain
prohibitive conditions and problems arise in the provision of known
four wheel drive systems which have thus far precluded their
employment in pneumatic tired commercial and passenger
vehicles.
If all four wheels are positively driven by the engine, a severe
amount of tire scraping or cornering scrub occurs as the vehicle
negotiates curves or turns. Under such conditions, the front wheels
must run through an arc of greater radius than that of the rear
wheels, and therefore tend to rotate faster than the rear wheels.
Further, in such a system, slight differences in effective wheel
radii caused by inevitable differences in tire inflation, tread
wear or variations in loading result in the occurrence of what is
known as circumferential scrub. Under such conditions, the wheels
having smaller radii necessarily tend to rotate faster than those
having larger radii while traversing the same distance. If the
wheels are positively driven together at the same angular speed by
the drive system, then on corners the front wheels are bodily
scraped over the ground, and on straight travel the wheels having
smaller radii are scraped. Tires will not long withstand such
abuse. In addition, undue stresses or windup occurs in the driving
parts and fuel consumption is excessive.
One approach to solving the problems inherent in such a system is
to provide a manually operable clutch or disengageable gear
enabling the front wheels of the vehicle to be selectively engaged
or disengaged for positive drive effort. Thus, the front wheels
would only be locked into engagement for four wheel drive when
surface conditions would permit. Such engagement would normally
occur when the vehicle was traveling on unpaved surfaces. When the
vehicle was traveling over paved surfaces, the front wheels would
be disengaged and the standard rear wheel drive would propel the
vehicle.
Much effort has been devoted to another approach which is providing
a third differential in a four wheel drive system such that front
and rear drive shafts would serve respectively to drive front and
rear differentials, the shafts being powered from the engine
through a center or third differential. Such a differential system
clearly permits overspeeding of any one or more of the wheels as a
result of rounding corners or of certain wheels having a smaller
effective radius than others.
Certain problems however, arise in connection with this type of
system. For instance, if one set of wheels should encounter a
slippery or icy patch of ground and lose all traction, they will
spin freely and the differential action will cause the other set of
wheels to exert no driving torque. Manually operable locking means
have been incorporated into such three differential systems which,
when engaged, eliminate differential action between the drive shaft
and positively lock the driven parts together. These are, however,
inherently so limited in effectiveness that they have never found
any commercial acceptance.
Other four wheel drive systems have been proposed which incorporate
a center differential which will automatically provide for locking
out or inhibiting differential action whenever limited free ranges
of differential action are exceeded. Such devices are operative to
automatically restore such action when the tendency to exceed the
range ceases. One such system is shown and described in U.S. Pat.
No. 2,796,941 issued to Claude Hill.
As will be apparent, however, such a system requires the addition
of many structural elements and results in a mechanism which is
both costly and cumbersome.
The present invention is directed to providing a torque transfer
mechanism which in the forward mode of operation will allow the
front wheels to overspeed the rear wheels by any amount but will
allow the rear wheels to overspeed the front wheels only by a
predetermined minimum amount. The predetermined minimum amount will
be determined as that amount necessary to compensate for
differences in wheel radii or tire wear. The torque transfer
mechanism of the present invention in the reverse mode of operation
provides a drive torque to one drive axle with only a reduced
amount of torque being transferred to the other drive axle.
This invention is adapted to provide such a result with the
addition of a minimum number of operating parts and is further
adapted to provide such a result in a most economical manner.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of one embodiment of the present
multiple path drive system shown schematically on an automotive
vehicle.
FIG. 2 is an enlarged view partially in section of the torque
transfer mechanism.
FIG. 3 is a diagrammatic view of a portion of FIG. 2 showing an
alternative embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
There is illustrated in FIG. 1, one type of automotive vehicle
wherein the torque transfer mechanism of the present invention is
particularly useful. The vehicle includes a prime mover 10 and an
automatic transmission 11 connected to the prime mover. A torque
transfer mechanism 12 is connected to the transmission 11 and is
adapted to transmit torque to a front drive axle assembly 13
through a torque transmitting member here shown as a drive shaft 15
and to a rear drive axle assembly 16 through a torque transmitting
member here shown as a drive shaft 17. The front axle assembly 13
and rear axle assembly 16 are adapted to drive front and rear pairs
of traction wheels 20 and 21 respectively.
Referring now to FIG. 2 in which one embodiment of the torque
transfer mechanism 12 is shown, the torque transfer mechanism
includes a housing generally referred to as 22. A portion of the
input shaft 23 is shown which is driven by the transmission 11.
Driven by the shaft 23 is a planetary carrier 26 which forms one
element of a differential gear mechanism 25.
The differential gear mechanism 25 includes the planetary carrier
26, a plurality of planetary gears 27 on the carrier 26, a sun gear
28 positioned concentric to and overlying the input shaft 23, and a
ring gear 30 also positioned concentric to the central axis of the
input shaft 23. Attached to the sun gear 28 for rotation therewith
is a sleeve section 31 concentric to and overlying the shaft 23.
The sleeve section 31 is adapted to rotate relative to the input
shaft 23. Attached to the ring gear 30 is a supporting member 36
including a hub portion 37 having a central axis common to the
input shaft 23. Attached to the hub portion 37 and axially
extending therefrom is a hollow shaft 38 adapted to be connected to
the drive shaft 17.
Disposed between the planetary carrier 26 and the sleeve section 31
of the sun gear 28 is a one-way driving means 40, here illustrated
schematically as a sprag clutch. The sprag clutch is oriented to
allow the sleeve section 31 to overspeed the planetary carrier 26
in one direction of rotation, that direction corresponding to the
direction of rotation of the components when the vehicle is
traveling in a forward direction. If the planetary carrier tends to
overspeed the sun gear in the forward direction of rotation, the
one-way driving means would lock the elements together thereby
preventing differentiation between them.
A rotary drive element 41 here shown as a spur gear overlies sleeve
section 31 in splined engagement therewith. Disposed in the lower
end of the housing 22 is an output shaft 42 adapted to be connected
to the drive shaft 15. An annular hub member 39 is splined to the
output shaft 42 for rotation therewith. Also disposed in the lower
end of the housing 22 is a rotary drive member 43 journaled for
rotation in bearings 46 and connected to the rotary drive element
41 by means of a drive chain 44.
A friction clutch 45 is disposed between the rotary drive member 43
and the output shaft 42. The clutch 45 includes a series of
longitudinal splines 50 defined in the rotary drive member 43.
Positioned in the splines 50 are a series of friction discs 51. A
similar series of splines 52 are defined in the hub member 39. A
similar series of friction discs 53 are disposed in the splines 52
in the hub member 39, and when assembled, are interleaved between
the friction discs 51.
An annular pressure applying means 55 overlies the output shaft 42
and is positioned internal to the periphery of the rotary drive
member 43 and adjacent to an end wall 56 thereof. The pressure
applying means 55 is axially slidable with respect to the end wall
56. A pressure chamber 57 is defined by and between the pressure
applying means 55 and the end wall 56.
The automatic transmission 11 includes a source of fluid pressure
60, the structure and function of which are more clearly set forth
in U.S. Pat. No. 3,165,946 issued to R. W. Wayman. The equivalent
pressure source in that patent is identified by number 160 and
called the front pump. Such a pressure source is common to almost
every type of automatic transmission.
The pressure source 60 is shown in FIG. 2 connected to a forward or
front clutch 61 of the automatic transmission 11 by means of a
conduit 62. Valve means (not shown) associated with the pressure
source 60 and transmission 11 are operative such that when the
transmission is conditioned for forward drive operation, the valve
means will direct fluid from the pressure source 60 to the front
clutch 61 through conduit 62. The operation of such a valve means
is shown and described in Column 23 of the previously mentioned
Wayman U.S. Pat. No. 3,165,946. The valve is referred to as "manual
selector valve 164". A conduit 63 connects the conduit 62 to a
fluid inlet 65, defined in a cap 66 connected to the housing 22. A
fluid conduit 67 is defined in the output shaft 42 and is in fluid
communication with the fluid inlet 65 by means of a tubular member
68. A conduit 70 is defined by the output shaft 42, and connects
the conduit 67 to a conduit 71 formed in the rotary drive member 43
which in turn is in communication with the pressure chamber 57.
A modified form of the hydraulic apply system is illustrated in
FIG. 3. This system includes a separate manual selector valve 75
connected to the pressure source 60 by means of a conduit 76. The
selector valve 75 is connected to the transmission shift linkage
(not shown).
A valve assembly 78 is shown disposed between the manual selector
valve 75 and the fluid inlet 65, the purpose of which will soon
become apparent. The valve assembly 78 includes a housing 80,
defining a pair of inlet ports 81 and 82 and an outlet port 83. The
housing 80 further defines a pair of cylindrical bores 85 and 86
which bores are coaxial and in fluid communication with inlet ports
81 and 82 and outlet port 83. Bore 85 is of larger diameter than
bore 86.
A valve member 87 including a land section 88, a land section 90
and a spool section 91 is shown slidably disposed within the
housing 80, the land section 88 being within bore 85 and the land
section 90 lying within bore 86. A pressure chamber 92 is defined
in the bore 85 between an end 93 of the valve member 87 and an end
95 of the bore 85. A port 96 is formed in the housing 80 in
communication with the pressure chamber 92. A bore 97 is defined in
the housing 80 and houses a pressure chamber 98. An inlet port 100
is formed in the housing 80 in communication with the pressure
chamber 98. A spring 101 is disposed in the bore 97 acting against
the valve member 87.
The valve assembly 78 is in fluid communication with the manual
selector valve 75 alternately through a fluid conduit 102 or a
fluid conduit 103. A conduit 104 connects the manual selector valve
75 and the forward clutch 61. A conduit 106 connects the conduit
102 to inlet port 100. A conduit 107 connects the conduit 103 to
inlet port 96.
The operation of the four wheel drive system shown in FIGS. 1 and 2
and described herein is as follows.
When forward motion of the vehicle is desired, the transmission
selector lever is placed in one of the forward drive positions. The
pressure source 60 is hydraulically connected in the clutch
applying circuit through the valve means (not shown) such that it
is operative to supply fluid pressure to the forward or front
clutch 61 of the transmission 11 through conduit 62 and also to
pressure chamber 57 of the friction clutch 45 through conduits 63,
68, 67, 70 and 71. The fluid pressure acts against pressure
applying means 55 urging it axially to the left as shown in FIG. 2,
thereby placing the friction clutch 45 in an engaged condition
whereby torque can be transmitted from the rotary drive member 43
to the output shaft 42.
An input torque is delivered to the torque transfer mechanism 12
through the input shaft 23. The input shaft 23 rotates the planet
carrier 26 which through the planet gears 27 distributes torque
between the sun gear 28 and the ring gear 30. The ring gear 30,
through supporting member 36, hub portion 37, and shaft 38 drives
the drive shaft 17, the rear axle assembly 16 and ultimately the
rear pair of traction wheels 21.
The sun gear 28 rotates the sleeve section 31, the rotary drive
element 41 and, through the chain drive 44, the rotary drive member
43. The drive element 43 through the friction clutch 45 drives the
hub member 39 and the output shaft 42, which drives the front drive
shaft 15, the front drive axle assembly 13 and ultimately the front
pair of traction wheels 20.
The geometry and design of the rotary drive elements 41 and 43,
here shown as spur gears is such that gear 43 is of a slightly
larger diameter than gear 41 and accordingly, has a greater number
of teeth. For purposes of example, gear 41 is shown with 41 teeth
and gear 43 with 43 teeth. Assuming now that the vehicle is being
driven under normal straight ahead driving conditions, the front
and rear pairs of traction wheels will be rotating at the same
speed, which will cause the sun gear 28 to overspeed the planetary
carrier 26 and the ring gear 30 by a predetermined percent. The
one-way driving means 40 is oriented such that it will allow this
overspeed when the vehicle is being driven in the forward mode of
operation.
If the vehicle encounters a curve or must negotiate a turn which
requires that the front wheels overspeed the rear by virtue of the
larger arc through which they must travel, the sun gear 28 will
overspeed the planetary carrier 26 and ring gear 30 by a still
greater percent.
If conditions exist due to differences in tire or wheel radii that
the rear wheels are overspeeding the front by a slight amount, the
net effect on the differential gear system will be to increase the
speed of the ring gear and planetary carrier thereby reducing the
relative overspeed of the sun gear with respect to the planetary
carrier and the ring gear. Such rear wheel overspeed will be
allowed by the one-way driving means 40 until the planetary carrier
is rotating at the same speed as the sun gear.
Under conditions where an excess amount of torque is supplied to
the drive axles for a given road coefficient, the wheels carrying a
lighter load will begin to slip. In standard front-engine vehicles,
the rear wheels carry appreciably less weight than the front wheels
and consequently will lose traction and slip before the front
wheels. If such relative slippage of the rear wheels relative to
the front wheels exceeds the design limit of 4- 5 percent, the
planetary carrier will tend to overspeed the sun gear locking up
the one-way driving means and preventing any differentiation
between the carrier and sun gear. If that situation occurs, the
ring gear 30 will transmit torque to the planetary carrier 26, and
through the one-way driving means 40 to the sun gear 28, the rotary
drive elements 41 and 43, and the friction clutch 45 to the output
shaft 42 and then to the front pair of traction wheels 20.
This transfers any additional torque which the rear wheels are
unable to effectively utilize to the front pair of traction wheels
in accordance with the road coefficient of friction versus percent
slip at each drive axle. At a limiting value of total torque
transmitted, both the front and rear axles will be utilizing
substantially the maximum available tractive effort.
Thus a multiple path drive system has been provided which allows
the front wheels to overspeed the rear wheels by any amount but
which allows the rear wheels to overspeed the front wheels by only
a predetermined percent at which point the differential gear
mechanism will lockup transferring additional torque to the front
wheels.
Absent the hydraulic apply system of the present invention, serious
problems would occur when the vehicle was driven in the reverse
direction. The one-way driving means would lockup for any tendency
of the sun gear 28 to overspeed the planetary carrier 26 in the
reverse direction which overspeed is inherent in the system as
designed. The lockup would result in a tire scrub of approximately
5 percent and/or constant slippage in the friction clutch 45.
As previously described, however, the pressure source 60 is
connected to the clutch applying circuit to provide fluid pressure
for clutch engagement only when the transmission is in a forward
mode of operation. When the gear selector lever of the automatic
transmission 12 is placed in the reverse position, the pressure
source 60 communicates no fluid pressure to the pressure chamber
57. The pressure applying means 55 moves axially to the right as
shown in FIG. 2, releasing the friction clutch 45. In this mode of
operation, torque is transmitted to the rear wheels only.
If the vehicle encounters conditions where it must be moved in
reverse and the rear wheels are on a slippery surface, some torque
will be transferred to the front wheels due to the slight inherent
drag of the friction clutch 45.
The operation of the embodiment shown in FIG. 3 is substantially
the same as for the embodiment shown in FIG. 2 and described herein
except that the pressure source 60 is hydraulically connected in
the clutch applying circuit such that the pressure source is
operative to provide fluid pressure to the clutch engaging circuit
in both forward and reverse and valve means are provided for
applying a limited and substantially reduced amount of pressure to
the pressure chamber 57 of the friction clutch 45 in the reverse
mode of operation.
In the forward mode of operation, the pressure source 60 supplies
fluid pressure to the manual selector valve 75 and then to the
forward clutch 61 through conduit 104 and to valve assembly 78
through conduit 102. Fluid is also communicated to pressure chamber
98 through conduit 106 where it acts against the valve member 87 to
urge it to the left as viewed in FIG. 3, thereby uncovering the
entrance port 81 and blocking the entrance port 82. Fluid flows
through the valve assembly from the entrance port 81 to exit port
83 and then to fluid inlet 65 to act to engage the friction clutch
45 as previously described.
In the reverse mode of operation, the pressure source 60 supplies
fluid pressure to the manual selector valve 75 and then to the
valve assembly 78 through conduit 103. Fluid is also communicated
to pressure chamber 92 through conduit 107 where it acts against
the valve member 87 to overcome the force of the spring 101 and
urge the valve member to the right as viewed in FIG. 3. As valve
member 87 moves to the right, the entrance port 82 is uncovered.
Land section 88 partially blocks the outlet port 83 resulting in a
substantially diminished pressure being transmitted to the pressure
chamber 57 and thus the friction clutch 45 is only lightly engaged.
Any tendency to import tire scrub to the vehicle wheels will be
absorbed by slipping of the clutch.
Various of the features of the invention have been particularly
shown and described, however, it should be obvious to one skilled
in the art that various modifications may be made therein without
departing from the scope of the invention.
* * * * *